(a) Trustees shall discharge their duties with respect to the 401(a) plans for the exclusive purpose of providing benefits to participants and their beneficiaries;
(b) Trustees shall diversify fund investment so as to minimize the risk of large losses unless, under the circumstances, it is clearly prudent not to do so;
(c) Trustees shall defray reasonable expenses of investing and operating the funds under management; and
(d) Trustees shall discharge their duties in accordance with the documents and instruments governing the trusts or other funds under management insofar as the documents and instruments are consistent with the provisions of this article.
(e) The duties of the board apply only with respect to those assets deposited with or otherwise held by it.